This invention relates to an object lens head assembly and more particularly to a mechanism for positioning an object lens relative to an optical recording disc used in an optical disc apparatus.
FIGS. 1 to 3 illustrate one example of a related optical head assembly or a mechanism for positioning an object lens to which the present invention may be applied and which is disclosed in U.S. Pat. No. 4862441 (Japanese Patent application No. 61-120074). FIG. 1 is a plan view of the object lens head assembly, FIG. 2 is a sectional view taken along line II--II of FIG. 1, and FIG. 3 is a side view of the object lens head assembly with an information conversion apparatus omitted.
In these figures, reference numeral 1 designates a magnetic circuit of a linear motor for reciprocatingly driving an object lens in the radial direction (the direction of an arrow A) of a disc 11 shown in partial cutaway view, 2 is a drive coil, 3 is a coil bobbin, 4 is a transducer shown as an information conversion apparatus for the conversion between the information in an electrical signal and the information in a light beam, 5 is a reflective mirror for reflecting the light beam generated from the information conversion apparatus 4 toward an object lens 6 which is for collecting the light beam, 7 is an actuator for positioning the object lens 6 along a direction perpendicular to the disc for accurately collecting the light beam to produce a light spot on the disc 11, and 9 is the light beam.
With this object lens head assembly, the object lens 6 and the reflective mirror 5 are positioned in the radial direction of the disc 11 (direction of the arrow A) by the linear motor. The light beam 9 generated from the information conversion apparatus 4 is reflected by the reflective mirror 5 to perpendicularly impinge upon the object lens 6, where it is collected to form a light spot on the disc surface. At this time, the actuator 7 positions the object lens 6 in the direction perpendicular to the disc 11 so that the light spot is accurately formed on the disc surface.
Since the above-described object lens head assembly is provided with only a single object lens, the object lens must move over a complete stroke which corresponds to the width dimension of the information recording area of the disc or the radial dimension of the area in which recording tracks are formed. Therefore, a large-sized linear motor having a large drive force must be used in order to shorten the access time, resulting in a large-sized optical head assembly.